1. Field of the Invention
Lens manufacturing apparatus with particular reference to plastic lens shaping molds.
2. Discussion of the Prior Art:
Lens blanks of thin plastic flat stock may be heated and formed to meniscus shapes by slumping, pressing or urging with partial vacuum against a cupped shaping surface. In order to avoid lens surface marring by occurrences of machine marks, scratches or air-borne contaminents on the shaping surfaces they are customarily cushioned with a thin, smoothly surface layer of rubber. However, while serving to relieve at least some of the problems of lens surface marring, this mold surface treatment is not conducive to free sliding of a lens blank over the shaping surface during its being brought from flat to a curved shape and occurrences of less than optimum conformance to the shaping surface curvature (i.e. some flattening of centermost positions of blanks from expected curvature) have been problematic. Additionally, the tendency for sticking and need for deliberate picking of the finished lens blank tends to render mass production performance of the lens shaping operation tedious as well as abusive to the mold surface cushion. The need heretofor for frequent time consuming and costly repair and/or replacement of the mold surface cushion together with less than optimum accuracy of final lens surface curvature has left a long standing need for improvement in the art.
Attempts to overcome lens blank drag and sticking problems have included experimentation with and the use of release agent coatings including various powders and sprays most of which were found to be either damaging to the lens and/or mold surfaces or difficult to remove from the lens products as well as of short-term usefulness requiring re-application with each lens forming operation. At best, this approach to lens sticking problems involves a need for uneconomical extra operations of repeatedly treating the mold surfaces and/or cleaning of the lens products as well as the added cost and problem of inventorying separate mold release products.
Accordingly, an object of the present invention is to accomplish in plastic lens blank shaping operations a quick, residue-free lens release at shaping cycle end and optimum optical quality of lens blank surfaced texture, accuracy of intended lens geometry and long production run capabilities.
A further objective is to accomplish the foregoing in simple and economical fashion and, in particular, without the need for auxiliary release agents and/or end product residue removal operations.
Other objects and advantages of the invention will become apparent from the following description.